The aforementioned copending applications and issued patent, and the art cited in the files thereof or made of record directly in the application texts, including, for example, U.S. Pat. No. 3,847,438, disclose a variety of mechanical structures for forming trenches, mine galleries and like excavations in subterranean structures, primarily for the recovery of valuable minerals such as coal.
In general, these systems involve the application of a cutting structure to the full height of a gallery to be cut through the subterranean strata and which may be associated with timbering or support equipment which may be separate from or associated with the cutting tools. In some of the modern automatic or semiautomatic gallery cutting machines, roof timbering is braced against the roof of a previously cut portion of the gallery against a shoe or plate lying on the floor thereof and is braced by fluid-operated cylinders. A pivot arrangement mounts a rotary pick structure and can press this structure against the face of the gallery to be cut away while a conveyor removes the detritus.
While such systems have proved to be advantageous for many gallery-forming mineral-mining purposes, problems have been encountered in the formation of relatively flat, i.e. small-height channels or passages in the structure, i.e. in the opening of a crosscut between two shafts.
The term "passage" as used herein is intended to refer to the generally low-height chamber which must be opened before the major gallery-forming and mineral-recovery equipment, with its excavating machine and conveyor can be introduced or to remove coal where such machinery cannot be employed. It can also refer to ventilation passages and passages which can be used to carry away detritus or the recovered mineral matter and will usually be a passage connecting two galleries, a shaft and a gallery or two shafts. The passage is, therefore, referred to hereinafter as a crossdrift or crosscut and these terms will be understood to represent the passage as identified above and which will have relatively small height and relatively large width, i.e. width which can be many times the height. For example, the width can be several meters while the height is usually less than a meter. Thus a crossdrift or crosscut whose formation is the paramount purpose of the present invention is relatively flat, wide and long.
In the opening of a crossdrift in a subterranean structure it is desirable to use mechanized techniques to accelerate the process. However, for thin seams and the advance of the drift along the relatively narrow strata, there are no machines which have proved to be fully suitable to the present time. In general, the opening of the drift is effected by blasting techniques so that personnel must creep with increasing depth into the passage formed in the direction of advance of the drift, drill the desired explosive bores, pack the explosive in, creep back in the opposite direction, and detonate the charges. The coal or drift detritus dislodged from the advancing face of the drift must then be removed by hand with shovels. This is the procedure for advancing drifts of a height of 50 to 70 cm through correspondingly thin seams in coal mines.
Because of the need for direct access of the personnel to the advancing face of the drift, ventilating systems must be carried along together with conveyors and the like.
The advance of the drift is slow because of the need to support the drift with timbering, shuttering and the like. While many attempts have been made to mechanize this process, none of them have been fully successful.
In German patent document DE-OS No. 25 33 518, corresponding substantially to U.S. Pat. No. 4,095,845, there is described an apparatus which makes use of a new type of cutter which is gaining increasing interest in the mechanized advance of excavation in a subterranean setting.
This patent describes inter alia a tool having a helical flight and rotatable about the axis of the helix, the flight being formed with excavating picks which cuts away the coal face as the machine advances this cutter against the face. The excavating drum can be one of a plurality of such drums articulated together end to end and capable of being advanced individually or in groups to chisel away the face.
Each of the excavating drums or drum sections comprises a worm conveyor displacing the detritus axially in the direction of a conveyor which may be a bucket, trough, belt or flight conveyor advancing with the machine as the latter cuts away the face of the gallery wall.
The articulated excavating drums, with their helical conveyor ribs and chisels or picks at the periphery thereof are thus combined with a rearwardly extending conveyor to form a continuously advancing excavating machine whose cutting tools can be advanced against the strata to be cut away and recovered and which can be raised and lowered to excavate thick seams or veins.
While all of these mechanical systems have resulted in major advances in mining, especially coal mining, and rapid formation of galleries with recovery of the desired mineral matter they have not solved the problem of opening low-height cuts or passages as heretofore described as crossdrifts and crosscuts.